As gasoline prices have soared and concerns over harmful emissions have mounted in recent years, vehicles that run on alternative fuel sources are becoming increasingly important. For example, the use of compressed natural gas (“CNG”) as an alternative fuel for motor vehicles is becoming increasingly popular throughout the world because it is relatively inexpensive, burns cleanly, is relatively abundant and is adaptable to existing technologies.
Natural-gas vehicles use the same basic principles as gasoline-powered vehicles. In other words, the fuel (natural gas) is mixed with air in the cylinder of, e.g., a four-stroke engine, and then ignited by a spark plug to move a piston up and down. Although there are some differences between natural gas and gasoline in terms of flammability and ignition temperatures, natural-gas vehicles themselves operate on the same fundamental concepts as gasoline-powered vehicles. Accordingly, existing gasoline-powered vehicles may be converted to run on CNG, thereby easing the transition between gasoline and CNG in markets where gasoline-powered vehicles are dominant. In addition, an increasing number of vehicles worldwide are being originally manufactured to run on CNG.
Advantageously, CNG-fueled vehicles have lower maintenance costs when compared with other fuel-powered vehicles. In addition, CNG emits significantly fewer pollutants such as carbon dioxide, hydrocarbons, carbon monoxide, nitrogen oxides, sulfur oxides and particulate matter compared to petrol.
Despite the advantages of compressed natural gas as a motive fuel, the use of natural gas vehicles faces several logistical concerns, including fuel storage and infrastructure available for delivery and distribution at fueling stations. Natural gas suitable for vehicle use is customarily stored in small capacity tank, at 3,600 psi at 70° F., and is distributed from storage tanks to an on-vehicle receiving tank by “cascade filling.” Cascade filling is accomplished by starting out with the storage tank at a higher pressure than the receiving tank and then allowing this pressure to force the gas (or liquid) into the receiving tank. In so doing, natural gas is transferred, and the pressure in the storage tank drops to the point where the pressures of the two tanks become equal and nothing more is transferred.
The storage and distribution of CNG is severely affected, however, at low temperatures, and particularly when the temperature drops below 40° F. At low temperatures, the pressure in the storage tank drops, thereby resulting in less of a difference in pressure between the receiving tank and the storage tank, ultimately resulting in inefficiencies in gaseous fuel transfer (i.e., less gaseous fuel being transferred to the receiving tank on board the compatible vehicle, and longer filling times).
Moreover, the storage of CNG in large capacity tanks at high pressures is also problematic. In particular, storing CNG in tanks at 3,000-3,600 psi requires that the tank's walls be cast from thick steel or other suitable metal in order to withstand the enormous stresses caused by the compressed gas. As will be readily appreciated, large capacity CNG storage tanks would therefore be undesirably heavy and inefficient and expensive to manufacture and transport. As a result, transportation and storage of CNG is customarily effectuated by using numerous smaller, tube-shaped cylinders, which themselves are extremely heavy.
With the forgoing problems and concerns in mind, it is the general object of the present invention to provide a system and method for the cold-weather storage and distribution of gaseous fuels, which utilizes large capacity tanks that are insulative and have a reduced weight.